Spherical magnetic resonance imaging apparatus

ABSTRACT

In a magnetic resonance imaging apparatus, a transmitting/receiving coil is attached to a patient at a region of interest and disposed within a static magnetic field, a radio-frequency magnetic field, and a gradient magnetic field and an image of the patient is obtained. A tabletop is used to move the patient in the static field in a horizontal direction within a horizontal plane and up and down in a direction that is perpendicular to the horizontal plane, a patient couch controller causing the tabletop to move, based on the position of the region of interest obtained from the image so that the position of the region of interest is caused to coincide in three dimensions with center of the static magnetic filed and/or the gradient magnetic field.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic resonance imaging apparatus,especially useful for an open-type MRI apparatus that has an open magnetgantry.

2. Description of the Related Art

Earlier open-type MRI systems include a vertical field type MRI system(MRI system with open access to patient image volume), featuring openaccess to the patient image volume, as disclosed for example in U.S.Pat. No. 4,829,252.

In an MRI system featuring good open access, such as the above-notedvertical field type of open MRI system or a tubular type MRI system ofthe past with a short axis and large diameter, the patient couch ismoved front and back and to the left and right at a uniform height withrespect to the patient transport axis when acquiring images. In thiscase, in the open MRI system, there are not good gradient magnetic fieldlinearity and static magnetic field uniformity in comparison with theearlier tubular type MRI system. However, because there is good magneticfield uniformity at the center of the gradient magnetic field and staticmagnetic field, if images of the region of treatment of the patient areacquired at the center position of the magnetic field, high-qualityimages of the region of treatment are obtained. In this case, there isneeded a complicated process in which a mark from a positioningprojector is set on a specific point of the patient or T/R coil beforemoving the patient into the gantry as a preparation of setting thepatient on the center of the magnetic field. This is to inform the MRImain unit of distance information between the mark and the center of themagnetic field in a front/rear direction and a right/left direction withrespect to the patient transport axis.

When operating the above-noted type of open MRI as an interventionalapparatus, for example, the region (location) of treatment is often notlarge, but limited to a specific area. In the case, even if the patientcouch is moved within a horizontal plane with respect to the patienttransport axis at a uniform height, it was either extremely difficult orimpossible to position the region of treatment at the center of thegradient magnetic field and static magnetic field in three dimensions.

For this reason, the images obtained from such MRI systems in the pastexhibited a great deal of image distortion, image non-uniformities, andfat artifacts, making it difficult to use the images in treatment.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amagnetic resonance imaging apparatus which enables quick positioning ofthe region of treatment or diagnosis at the center of the gradientmagnetic field and static magnetic field, and enables the acquisition ofhighly precise, high-quality images, with reduced image distortion,non-uniformities, and fat artifacts.

In order to achieve the above-noted object, a magnetic resonance imagingapparatus according to the present invention comprises:

a static magnetic field generator for generating a static field;

a gradient magnetic field generator for generating a gradient magneticfield that is superimposed on the static magnetic field;

a radio-frequency magnetic field pulse transmitting/receiving unit,which applies a radio-frequency pulse to a region of interest of thepatient that is located within the static magnetic field, and which alsoreceives a magnetic resonance signal that is generated from the patient;

a patient couch, which enables movement of the patient;

a position information establishing apparatus which establishes positioninformation of the region of interest of the patient; and

a patient couch controller for moving the patient couch, based on theregion of interest position information, so that the region of interestis positioned either at the center of the static magnetic field, or atthe center of the gradient magnetic field.

According to the present invention, because a patient couch controllingmeans causes the movement of the movable patient couch, so as toposition the region of interest of the patient at the center of eitherthe static magnetic field or the gradient magnetic field, it is possibleto obtain precise, high-quality images, with reduced image distortion,non-uniformities, and fat artifacts.

Another aspect of the present invention is a method for performingmagnetic resonance imaging diagnosis, this method comprising the stepsof:

placing the patient onto a patient couch that is disposed within astatic magnetic field and a gradient magnetic field;

moving the patient couch approximately, based on a signal from aposition detector, so that the region of interest of the patientapproximately coincides with the center of the static magnetic field orthe center of the gradient magnetic field;

applying a radio-frequency pulse to the region of interest of thepatient, and receiving a magnetic resonance signal that is generatedfrom the patient;

reproducing a plurality of images of the patient, based on the magneticresonance signal;

selecting an image that includes the region of interest from theplurality of images of the patient; and

moving the patient couch, based on the selected image, so that theregion of interest of the patient coincides precisely with the center ofthe static magnetic field or the center of the gradient magnetic field.

The above-noted method of diagnosis according to the present inventionprovides the same effect as the earlier described magnetic resonanceimaging apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view that shows an outer view of an open-typeMRI apparatus according to the first embodiment of the presentinvention.

FIG. 2 is a system block diagram of the MRI apparatus according to thesecond embodiment of the present invention.

FIG. 3 is a drawing that shows the arrangement of the static fieldmagnet and the magnetic gradient coil.

FIG. 4A and FIG. 4B are drawings which show the horizontal movementmechanism of the patient couch which is provided in the MRI apparatusaccording to the first embodiment of the present invention.

FIG. 5 is a drawing that shows the vertical movement mechanism of thepatient couch which is provided in the MRI apparatus according to thefirst embodiment of the present invention.

FIG. 6A and FIG. 6B are drawings that illustrates the positioning of theregion of interest of the patient at the center of the static magneticfield and the center of the gradient magnetic field.

FIG. 7 is a drawing that shows a positioning scan.

FIG. 8 is a drawing that shows another embodiment of a patient couch,which includes a tabletop holding mechanism.

FIG. 9 is a perspective view of the tabletop of FIG. 8.

FIG. 10 is a cross-section view of the tabletop of FIG. 8.

FIG. 11 is a drawing that shows another embodiment of a verticalmovement mechanism of the patent transporter.

FIG. 12 is a drawing that shows the patient couch control system, whichincludes another embodiment of a vertical movement mechanism of thepatent transporter.

FIG. 13 is a system block diagram that shows an MRI apparatus accordingto the second embodiment of the present invention.

FIG. 14A and FIG. 14B are drawings that show the approximate positioningof the transmitting/receiving coil of the MRI apparatus of the secondembodiment of the invention at the center of the static magnetic fieldand center of the gradient magnetic field.

FIG. 15 is a drawing that shows a patient couch control system in ashort-axis, large-diameter magnetic or vertical-field type magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described in detailbelow, with reference to relevant accompanying drawings.

First Embodiment

FIG. 1 shows perspective outer view of an open-type MRI apparatusaccording to the first embodiment of the invention. In this drawing, thearrow A indicates the front direction as seen from the front of the MRIapparatus, the arrow B indicates the side direction, and the arrow Cindicates the top direction. Though a similar MRI apparatus is describedin Japanese Patent Application No. 9-112452, the present invention isnot limited by this shape of this MRI apparatus.

The main enclosure 1 (hereinafter generally referred to as the magnetgantry1), has within it such elements as a static field magnet, amagnetic gradient coil, and an excitation (RF) coil for use with respectto the entire body of the patient. A patient couch 2 can move freelyover the floor surface 13, and a tabletop 6, on which a patient P isplaced, is mounted to the top part of the patient couch 2.

The magnet gantry 1 is of spherical shape and, seen from the directionof arrow A, has a space 3 formed in it, this space having a width suchthat it is possible to insert the patient couch 2 into the center partof the magnet gantry 1. The center of the magnet gantry 1 has aspherically shaped inner space 5, which houses the patient couch 2,including the tabletop 6, and is of sufficient size as to allow therotation of the patient couch 2 in an arbitrary direction (for example,in the horizontal direction).

The patient couch 2 is provided with a rotational drive mechanism (notshown in the drawing) for the purpose of rotationally driving thetabletop 6, onto which the patient is placed, at least 90 degrees withinthe horizontal plane after the patient couch 2 is placed in the centerof the inner space 5.

An access port 7 through which the inner space 5 communicates with theoutside of the magnet gantry 1 is provided in the side part of themagnet gantry 1 as seen from the direction of arrow B. A similar accessport is also provided on the opposite side of the inner space 5.

The access port 7 allows passage of part of the tabletop 6 when thepatient couch 2 is housed within the inner space 5, and is of sufficientwidth to allow the patient P that is disposed horizontally to passthrough the center part on both sides, so as to position the region ofdiagnosis or region of treatment at the center of the magnet.

According to the above-noted configuration, it is possible for aphysician, for example, to enter the inner space 5 via the space 3formed in the magnet gantry 1, and possible for a physician, forexample, to approach the patient couch 2 onto which the patient P isplaced, from the side.

FIG. 2 shows a system block diagram of the MRI apparatus according tothe first embodiment of the present invention, and FIG. 3 shows thearrangement of the static field magnet and the magnetic gradient coil.In FIG. 2, the cross-section of the magnet gantry 1 as seen from thefrontal direction thereof is shown. In this case, by placing the patientcouch 2, inserted via the space 3, into the inner space 5 of the magnetgantry 1, and rotating the tabletop 6 by means of the rotational drivemechanism of the patient couch 2, the body axis of the patient P isaligned in the direction of the access port 7.

In the above condition (with the patient P in a condition that enablesimage acquisition), or before and after this condition, atransmitting/receiving (T/R) coil 19 is attached at, for example, thechest area of the patient P. The T/R coil 19 can be replaced by areceiver coil according to the purpose of the diagnosis.

The patient couch 2 can move the tabletop 6 forward and back, to theleft and right (horizontal directions) and up and down (verticaldirections), and is formed by a patient couch base 2 a, a horizontalmovement screw box 2 c, which has a horizontal movement mechanism forthe purpose of moving the tabletop 6 in a horizontal direction, and alinking section 2 b, which links the base 2 a and the horizontalmovement screw box 2 c of the patient couch 2 and which has a verticalmovement mechanism for the purpose of moving the tabletop 6 up and down.In FIG. 2, the center O indicates the center of the static magneticfield and the center of the gradient magnetic field the horizontalmovement mechanism and vertical movement mechanism will be describedbelow.

A static field magnet 21, as shown in FIG. 3, is disposed along thesubstantially spherical inner space 5, and is formed by a coil bundlemade of either a superconductor or a conventional conductor, throughwhich a circulating current passes, resulting in a magnetic field thatis uniform with respect to the body axis of the patient (Z axis) beingapplied to the patient P.

A magnetic gradient coil 23 is formed by an X-axis magnetic gradientcoil 23 x, a Y-axis magnetic gradient coil 23 y, and a Z-axis magneticgradient coil 23 z, these coils being driven by a magnetic gradientpower supply 17. These magnetic gradient coils apply gradient magneticfields Gx, Gy, and Gz, the magnetic field intensity of which varylinearly, in the X and Y directions within a desired cross-section ofthe patient P, and in the Z direction, which is perpendicular withrespect to the X and Y directions.

With this arrangement because the static field magnet 21 is providedalong the inner space 5, the coil pattern of the static field magnet 21is spherical, enabling enhancement of the uniformity of the staticmagnetic field developed by the static field magnet.

The above-noted MRI apparatus also has a system controller 14, atransmitting/receiving (T/R) unit 15, a patient couch controller 16, amagnetic gradient power supply 17, a reconstruction apparatus 18 a and adisplay apparatus 18 b. The T/R unit 15, under control from the systemcontroller 14, generates a radio-frequency magnetic field with respectto the patient P by applying a radio-frequency signal to the T/R coil19, receiving from the T/R coil 19 a magnetic resonance signal generatedfrom the patient P with the application of a static magnetic field, agradient magnetic field and a radio-frequency magnetic field, amplifyingand detecting the received signal, and then A/D converting and sendingthe signal to the reconstruction apparatus 18 a.

The reconstruction apparatus 18 a performs image configurationprocessing, including Fourier transformation, with respect to data inputto it from the T/R unit 15. The display apparatus 18 b displays across-sectional image of the patient P that was reconstructed by thereconstruction apparatus 18 a.

The patient couch controller 16, under the control of the systemcontroller 14, outputs movement information for the purpose of movingthe tabletop 6 to the patient couch 2, this information indicating theamount of horizontal movement of the tabletop 6 and the amount of up anddown movement of the tabletop 6.

The patient couch controller 16 outputs movement amount information tothe patient couch 2 for the purpose of moving the patient couch 2 sothat the center of the region of imaging (region of diagnosis or regionof treatment) of the patient P is caused to coincide with the center ofthe static magnetic field and center of the gradient magnetic field. Thepatient couch 2, in response to the movement amount information from thepatient couch controller 16, moves the tabletop 6 in the horizontal andvertical directions, using the horizontal movement mechanism andvertical movement mechanism.

(Horizontal Movement Mechanism)

FIG. 4A and FIG. 4B show the horizontal movement mechanism of thepatient couch that is provided in the MRI apparatus according to thefirst embodiment of the present invention. FIG. 4A provides a rear viewof the horizontal movement screw box and the horizontal movementmechanism that is provided on the tabletop. FIG. 4B provides a side viewof the horizontal movement screw box and the horizontal movementmechanism that is provided on the tabletop. The horizontal movementmechanism 24 is described below, with reference made to FIG. 4A and FIG.4B.

Referring to FIG. 4A, on the rear side of the tabletop 6 are formed tworows of front-to-back movement screw grooves 25, on the left and right,for the purpose of moving the tabletop 6 forward and back, andleft-to-right movement screw grooves 27, disposed between the two rowsof front-to-back movement screw grooves 25, for the purpose of movingthe tabletop 6 to the left and right.

Inside the horizontal movement screw box 2 c are provided front-to-backmovement screws 29, which is disposed so as to mesh with thefront-to-back movement screw grooves 25, and a left-to-right movementscrew 33, which is disposed so as to mesh with the left-to-rightmovement screw grooves 27. The front-to-back movement screw 29 and theleft-to-right movement screw 33 are mounted to a shaft 31.

According to a horizontal movement mechanism configured as noted above,when movement amount information that indicates an amount of horizontalmovement is sent from the patient couch controller 16, the screws 29 and33 rotate in response to this amount of horizontal movement informationsent from the patient couch controller 16. For this reason, the screwgrooves 25 and 27 that mesh with the screws 29 and 33 move, therebycausing the tabletop 6 to move within the horizontal plan (front-to-backand left-to-right), in response to the amount of horizontal movementthat was received.

(Vertical Movement Mechanism)

Turning to FIG. 5, we see the vertical movement mechanism that isprovided in the MRI apparatus according to the first embodiment of thepresent invention. As shown in FIG. 5, a vertical movement mechanism 34,which causes the tabletop 6 to move up and down, is provided on thetabletop 6.

The vertical movement mechanism 34 is formed by a first holding section35 a, which is mounted to one end of a hydraulic cylinder 34 a and whichis provided in the patient couch base 2 a, and a second holding section35 b, which is mounted to the other end of the hydraulic cylinder 34 aand which is provided in the horizontal movement screw box 2 c. Thehydraulic cylinder 34 a causes the horizontal movement screw box 2 c tomove up and down, with respect to the position of the patient couch base2 a, in response to hydraulic pressure.

According to a vertical movement mechanism 34 configured as noted above,when amount of movement information indicating the amount of verticalmovement is sent from the patient couch controller 16, the hydrauliccylinder 34 a, in response the amount of vertical movement informationfrom the patient couch controller 16, uses hydraulic pressure to causethe horizontal movement screw box 2 c to move up and down, via thesecond holding section 35, thereby enabling the up and down movement ofthe tabletop 6.

An MRI apparatus having the horizontal movement mechanism 24 and thevertical movement mechanism 34 configured as described above will now bedescribed. FIG. 6A and FIG. 6B illustrate the positioning of the regionof treatment of a patient placed in an MRI apparatus according to thefirst embodiment, so as to cause this region to coincide with the centerof the static magnetic field and the gradient magnetic field. FIG. 6Ashow the condition of the patient before performing positioning of theposition of diagnosis with the center of the magnetic field, and FIG. 6Bshows the condition of the patient after positioning the region ofdiagnosis with the center of the magnetic field.

When performing positioning of the region of diagnosis (or treatment)with the center of a magnetic field (static or gradient magnetic field)the T/R coil 19 is first attached at the region of diagnosis, such asthe chest part of the patient, as shown in FIG. 6A. Then, a manual ormechanical means is used to approximately align the tabletop 6 to theregion of diagnosis 30 of the patient P, so that the region of diagnosis30 is positioned in the area of the center O of the static magneticfield and gradient magnetic field by approximately positioning thetabletop 6.

Next, after approximate positioning of the tabletop 6, to facilitatepositioning of the region of diagnosis 30, the T/R unit 15,reconstruction apparatus 18 a, and display apparatus 18 b shown in FIG.2 are used to perform a high-speed positioning scan of a 2-dimensionalTlW multislice image, for example, in the horizontal direction near theregion of diagnosis 30 of the patient P, as shown in FIG. 7, therebyobtaining the multislice images S1 through S5 along the Z-axis (bodyaxis of the patient P).

Then, using a pointing device such as a mouse (not shown in thedrawing), a slice such as S4, which is the closest to the region ofdiagnosis 30, is selected. Essentially, after performing approximatepositioning of the region of diagnosis 30 within the horizontal plane, amultislice image is used to perform Z-axis positioning of the region ofdiagnosis 30. The pointing device is further used to select the regionof diagnosis 30 on the selected image to perform further positioning forX- and Y- axes.

Additionally, the system controller 14 outputs the position informationof the coordinates (x4, y4, and z4) of the region of diagnosis 30 in theselected slice image S4. Then, the difference (distance) componentsbetween the position information (corresponding to the region ofdiagnosis 30 position) of the image S4 that is sent from the patientcouch controller 14 and the position information for the center O of thestatic magnetic field and the gradient magnetic field are calculated,and then controls the patient couch 2 so as to move the tabletop 6 bythe calculated distance difference components.

When this is done, the horizontal movement mechanism 24 and the verticalmovement mechanism 34 move the tabletop 6 in the horizontal and verticaldirections, respectively, by the difference components, so that theregion of diagnosis 30 is quickly moved so as to coincide with thecenter O of the static magnetic field and the gradient magnetic field,as shown in FIG. 6B.

Essentially, because the uniformity of the static magnetic field and thelinearity of the gradient magnetic field are better the closer theposition is to the center O of these fields, by moving the patient couchin three dimensions, including vertical movement to that region so as toestablish the position of the region of diagnosis 30 at this center O,it is possible to obtain highly precise, high-quality images, withreduced image distortion, non-uniformities, and fat artifacts.

Additionally, by moving the patient couch up and down immediately beforeand after diagnosis and treatment, it is possible for a physician or atechnician to prepare or provide care to the patient P at an appropriateheight.

The setting of the position of the region of diagnosis 30 can be done,for example, by the operator pointing to the position 30 from amultislice image from the slice image S1 through the slice image S5, andcan also be performed automatically by means of image processing.

Another embodiment of the patient couch, which includes a tabletophorizontal holding mechanism, is shown in FIG. 8. FIG. 9 is aperspective view of the tabletop horizontal holding mechanism of FIG. 8.FIG. 10 is a cross-section view of the tabletop horizontal holdingmechanism of FIG. 8. The tabletop horizontal holding mechanism 35, asshown in FIG. 8, holds the tabletop 6 horizontally when the tabletop 6is moved forward and back with respect to the patient couch 2.

This tabletop horizontal holding mechanism 35 has a configuration suchas shown in FIG. 9. The horizontal movement screw box 2 c has the firstholding pin 37 a mounted to it, one end of the first supporting rod 36 aand the second supporting rod 36 b being mounted to this first holdingpin 37 a. The other end of the first supporting rod 36 a has the secondholding pin 37 b mounted to it, and the other end of the secondsupporting rod 36 b has the third holding pin 37 c mounted to it.

Side grooves 39 are formed on in the front-to-back direction on thetabletop 6, the second holding pin 37 b and the third holding pin 37 cfitting into these tabletop side grooves 39, so that when the tabletop 6move forward and back, the tabletop side grooves 39 move so that thesecond holding pin 37 b and the third holding pin 37 c slide therein.

According to a tabletop horizontal holding mechanism 35 configured asdescribed above, even if the tabletop 6 moves forward and back withrespect to the patient couch 2, the effect of the three holding pins,the first supporting rod 35 a, and the second supporting rod 36 b is tohold the tabletop 6, so that the tabletop 6 does not tip over. Thus, itis possible to perform work smoothly, without having the patient P tipover.

Another embodiment of the vertical movement mechanism of the patientcouch is shown in FIG. 11. FIG. 12 shows a patient couch control systemthat includes this embodiment of a vertical movement mechanism for thepatient couch.

The vertical movement mechanism 40 of the patient couch shown in FIG. 11is configured as follows. Vertical movement mechanism main units 49 areprovided at the bead end and at the feet end of the floor surface 47with respect to the patient P, a hydraulic cylinder 41 being disposedwithin each of these vertical movement mechanism main units 49.

A liner 51, which is mounted to the horizontal movement screw box 2 c isdisposed at the top ends of the two vertical movement mechanism mainunits 49, this liner 51 is supported at both of its ends by the verticalmovement mechanism 40. The tabletop 6 is disposed at the top of theliner 51. The hydraulic cylinders 41 use oil pressure to move the linerup and down.

The configuration of the horizontal movement mechanism is that of thehorizontal movement mechanism provided in the above-described horizontalmovement screw box 2 c.

According to a vertical movement mechanism 40 configured as describedabove and shown in FIG. 12, when movement amount information indicatingan amount of vertical movement is sent from the patient couch controller16, the hydraulic cylinders 41 move the liner 51 up and down by means ofhydraulic pressure, in response to the amount of vertical movement sentfrom the patient couch controller 16, thereby enabling up and downmovement of the tabletop 6.

Because of the double structure, having the liner 51 and the tabletop 6,which is supported by the liner 51 and which moves with respect to theliner 51, there is no tilting over of the tabletop 6. Thus, the patientP is not tilted over, and work can be performed smoothly.

Second Embodiment

FIG. 13 shows a system block diagram of an MRI apparatus according tothe second embodiment of the present invention. In this embodiment, whenperforming positioning of the region of diagnosis with the center O ofthe magnetic field (static magnetic field or gradient magnetic field) amanual or motorized mechanical means is used to automatically performapproximate positioning of the tabletop 6.

For this reason, the MRI apparatus of the second embodiment has a systemcontroller 14 a, a T/R unit 15, a patient couch controller 16 a, amagnetic gradient power supply 17, a position sensing unit 52, a3-dimensional position sensor transmitter 53, and a 3-dimensionalposition sensor receiver 55.

As shown in FIG. 13, the T/R coil 19 that is attached to the region ofdiagnosis of the patient P has the 3-dimensional (or 2-dimensional)position sensor transmitter 53 mounted to it. A 3-dimensional positionsensor receiver 55 is mounted, for example, at the center of the linkingsection 12 (position corresponding to directly above the magnetic fieldcenter O).

The 3-dimensional position sensor receiver 55 receives positioninformation that is sent from the 3-dimensional position sensortransmitter 53. The position sensing unit 52 accepts the positioninformation of the 3-dimensional position sensor transmitter 53 that wasreceived at the 3-dimensional position sensor receiver 55, and sendsthis information to the system controller 14 a.

The system controller 14 a sends the position information of the3-dimensional position sensor transmitter to the patient couchcontroller 16 a. The patient couch controller 16 a calculates thedifference (distance) components between the position information of the3-dimensional position sensor transmitter 53 that was sent from thesystem controller 14 a and the position information of the center O ofthe static magnetic field and gradient magnetic field, and controls thepatient couch 2 so as to move the tabletop 6 by the amounts indicated bythese difference components.

In the above-noted embodiment, instead of the 3-dimensional positionsensor transmitter 53, it is possible to provide a passive type ball oractive-type of light receiver, and instead of the 3-dimensional positionsensor receiver 55 to provide the transmitter of an optical positionsensor. The transmitter can also be provided on the top part of theaccess port 7 at the front and rear of the magnet gantry 1 (refer toreference numerals 55A and 55B).

The operation of a MRI apparatus of the second embodiment, configured asdescribed above, is as follows. FIG. 14A and FIG. 14B illustrate theapproximate positioning of the T/R coil of an MRI apparatus of thesecond embodiment at the center of static magnetic field and gradientmagnetic field. FIG. 14A shows the condition of the patient P beforeperforming approximate positioning of the T/R coil at the center of themagnetic field, and FIG. 14B shows the condition of the patient P afterapproximate position of the T/R coil at the center of the magneticfield.

First, as shown in FIG. 14, when position information is sent by the3-dimensional position sensor transmitter 53, the 3-dimensional positionsensor receiver 55 receives this position information, and the positionsensing unit 53 detects the position information of the 3-dimensionalposition transmitter 53 that was received by the 3-dimensional positionsensor receiver 55.

Next, the patient couch controller 16 a calculates the difference(distance) components from the position information (that is, the centerposition of the T/R coil 19 that is attached to the region of diagnosis30) of the 3-dimensional position sensor transmitter 53 sent from thesystem controller and the position information of the center O of thestatic magnetic field and the gradient magnetic field and, in order tomove the tabletop 6 by just these difference components, moves thetabletop 6 by the amounts of movement (difference components) sent fromthe patient couch controller 16 a, thereby moving the T/R coil 19 to theappropriate position, this being the approximate center O of themagnetic field.

In this manner, because the second embodiment of the MRI apparatusaccording to the present invention can make an approximate move of theT/R coil 19 to the center of the magnetic field automatically, it ispossible to reduce the work load on the operator.

Additionally, after the T/R coil 19 is approximately positioned at thecenter O of the magnetic field, it is possible as shown in FIG. 7 toperform positioning of the region of diagnosis 30 by means of apositioning scan, so that by merely moving the tabletop 6 by the amountof the difference components between this region of diagnosis 30position and the magnetic field center O, it is possible to quickly movethe region of diagnosis 30 to the center O of the magnetic field.

With the second embodiment of the present invention, it is thereforepossible to obtain highly precise, high-quality images, with reducedimage distortion, non-uniformities, and far artifacts. Furthermore, bymoving the patient couch up and down immediately before and afterdiagnosis and treatment, it is possible for a physician or a technicianto prepare or provide care to the patient P at an appropriate height.

If an image of the position of the T/R coil, which is attached to thepatient P, is obtained at a point that is removed from the center O ofthe magnetic field and different from the above-described positionsensor, discrimination is facilitated because of the weakness of themagnetic resonance signal. By using this phenomenon, it is possible toperform approximate movement of the tabletop 6 at the point at which themagnetic resonance signal reaches a given point, while repeatedly movingthe imaging and horizontal movement of the tabletop 6.

A variation on the above-noted embodiment is as follows. FIG. 15 shows apatient couch control system in a short-axis, large-diameter magnet or avertical-field type magnet. The patient couch control system is avariation that is suitable for use in applying the present invention toan MRI apparatus with good open access as used in the past, of thetubular, short-axis, large-diameter magnet type.

The above-noted patient couch control system has a tubular-typeshort-axis, large-diameter magnet 61, a tubular-type magnetic gradientcoil 63, a patient couch 63, a horizontal movement screw box 2 c thathas a horizontal movement mechanism, hydraulic cylinders 41 that have avertical movement mechanism, and a patient couch controller 16.Additionally, in order to detect the position of the patient P, it ispossible to provide a passive-type ball or an active-type light receiver67 at the top pan of the T/R coil 19, and to provide an optical positionsensor transmitter at the front and rear of the magnet 61. According toa patient couch control system configured in this manner, it is possibleto obtain the same type of effect that is obtained by theabove-described first and second embodiments.

It will be appreciated by a person skilled in the art that the presentinvention is not limited to the above-described embodiments, and cantake be embodied as various other variations thereof.

What is claimed is:
 1. A magnetic resonance imaging apparatuscomprising: a static magnetic field generator which generates a staticfield; a gradient magnetic field generator which generates a gradientmagnetic field that is superimposed on the static magnetic field; a mainenclosure having a spherical shape, formed so as to enable enclosing ofa patient, the main enclosure including the static magnetic field andthe gradient magnetic field; a radio-frequency magnetic field pulsetransmitting/receiving unit, which applies a radio-frequency pulse to aregion of interest of a patient that is located within the staticmagnetic field, and which also receives a magnetic resonance signal thatis generated from the patient; a patient couch, which enables movementof the patient in the main enclosure; a position informationestablishing apparatus which provides 3-dimensional position informationof the region of interest of the patient; and a patient couch controllerwhich moves the patient couch, based on the provided positioninformation, so that the region of interest is re-positioned in3-dimensions substantially either at the center of the static magneticfield, or at the center of the gradient magnetic field.
 2. A magneticresonance imaging apparatus as in claim 1, wherein the positioninformation establishing apparatus accepts input position informationbased on an image of the patient that is obtained from the magneticresonance signal.
 3. A magnetic resonance imaging apparatus as in claim1, wherein the position information establishing apparatus comprises aposition detection apparatus that detects the position of the region ofinterest.
 4. A magnetic resonance imaging apparatus as in claim 3,wherein the patient couch controller performs an initial approximatepositioning of the patient couch, based on a signal from the positiondetection apparatus.
 5. A magnetic resonance imaging apparatus as inclaim 1, wherein the patient couch is capable of moving the patient inthe horizontal and vertical directions.
 6. A method for performingmagnetic resonance imaging diagnosis in a magnetic resonance imagingapparatus having a main enclosure of spherical shape enabling enclosureof a patient, said method comprising: placing the patient onto a patientcouch that is disposed within a static magnetic field and a gradientmagnetic field formed in the main enclosure; moving the patient couchbased on a signal from a position detector so that a region of interestof the patient approximately coincides with the center of the staticmagnetic field or the center of the gradient magnetic field; applying aradio-frequency pulse to the region of interest of the patient, andreceiving a magnetic resonance signal that is generated from thepatient; reconstructing a plurality of images of the patient, based onthe magnetic resonance signal; selecting an image that includes theregion of interest from the plurality of images of the patient; andmoving the patient couch, based on the selected image, so that theregion of interest of the patient substantially coincides in3-dimensions with the center of the static magnetic field or the centerof the gradient magnetic field.
 7. A method for performing magneticresonance imaging diagnosis as in claim 6, wherein the step of selectingan image further comprises a step of designating the region of interestwithin the selected image.
 8. A method for performing magnetic resonanceimaging diagnosis, said method comprising: placing a patient onto apatient couch that is disposed within a main enclosure having aspherical shape, containing a static magnetic field and a gradientmagnetic field; designating a 3-dimensional position of a region ofinterest of the patient; and moving the patient couch, so that theregion of interest of the patient substantially coincides3-dimensionally with the center of the static magnetic field or thecenter of the gradient magnetic field.
 9. A method as in claim 8,wherein the step of designating a 3-dimensional position of a region ofinterest further comprises the steps of: moving the patient couch sothat the region of interest of the patient approximately coincides withthe center of the static magnetic field or the center of the gradientmagnetic field; applying a radio-frequency pulse to the region ofinterest of the patient, and receiving a magnetic resonance signal thatis generated from the patient; reconstructing a plurality of images ofthe patient, based on the magnetic resonance signal; selecting an imagethat includes the region of interest from the plurality of images of thepatient; and designating the region of interest within the selectedimage.
 10. A method as in claim 9 wherein the initial step of moving thepatient couch comprises obtaining positional information from a positionsensor representing a 3-dimensional position for the region of interest.11. A method for three-dimensionally positioning a patient region ofinterest substantially as an optimum MR imaging position for diagnosticimaging within an MRI system including a main enclosure having aspherical shape, said method comprising: positioning a patient region ofinterest at a first position within an MRI field of view; generating MRimages of the patient in three dimensions while located at said firstposition using a first high speed positioning scan MRI data acquisitionpulse sequence; locating and designating the patient region of interestposition within said images; generating 3-dimensional positiondifference data between the designated position of the patient region ofinterest in the images and an optimum MR imaging position; automaticallyre-positioning the patient region of interest in 3-dimensions from saidfirst, now designated, position to an optimum MR imaging position usingsaid position difference data; and generating diagnostic MRI data, afterthe patient is re-positioned to said optimum MR imaging position, usinga second diagnostic MRI data acquisition pulse sequence, different thansaid first sequence, to provide diagnostic images having improvedprecision and quality with reduced image distortion, non-uniformitiesand fat artifacts.
 12. A method as in claim 11 wherein said positioningstep utilizes position data provided by a position sensor thatautomatically senses a relative spatial position between a movablepatient and a fixed MRI system.